During cold start of an internal combustion engine, the temperature of a NOx reduction catalyst and other components in the aftertreatment system may be insufficient for efficient or effective operation to remove NOx and other constituents from the exhaust gas. For example, a selective catalytic reduction (SCR) catalyst may be insufficient to initiate NOx conversion or to provide efficient NOx conversion at cold start or low temperature operating conditions. Therefore, NOx storage catalysts have been adopted that meet increasingly stringent emissions control requirements during cold start conditions. These NOx storage catalysts temporarily store NOx during cold start conditions and release NOx and hydrocarbons at higher temperatures when the downstream SCR device is effective for immediate NOx conversion. The NOx and hydrocarbons released from the NOx storage catalyst are treated at a downstream NOx reduction catalyst.
While NOx storage catalysts have improved reduction of NOx and HC emissions during cold start and low temperature operating conditions, there remain deficiencies in their implementation. For example, if engine operations are terminated while the NOx storage catalyst has little or no storage capacity, then NOx and hydrocarbon storage capabilities are not available during a subsequent cold start. Therefore, further contributions in this area are needed.